This invention relates generally to an electromagnetic coupling such as a clutch or brake and, more particularly, to an armature assembly for such a coupling.
Newton U.S. Pat. No. 4,493,407 discloses a typical electromagnetic clutch in which an armature is connected to a driven hub by a mounting plate and is adapted to be frictionally coupled to a driving rotor when an electromagnet is energized to engage the clutch. Upon energization of the electromagnet, magnetic flux cuts across an air gap between the rotor and the armature and attracts the armature into engagement with the rotor. The armature is rotated by the rotor and acts through the mounting plate to rotate the driven hub.
In clutches of the type disclosed in the Newton patent, the armature is connected to the mounting plate by a series of leaf springs which couple the armature and mounting plate for rotation in unison while allowing the armature to move toward and away from the rotor when the electromagnet is energized and de-energized. Each spring usually is riveted at one end to the armature and at the other end to the mounting plate. Rubber bumpers are carried by the mounting plate and contact the armature to hold the mounting plate and the armature out of engagement with one another and thereby establish a flux barrier between the two.
Torsional shock occurs when the clutch is first engaged and torsional spikes are created during steady state operation of the clutch. In order to dampen the torsional shock and to smooth the spikes, the clutch of the Newton patent utilizes an elastomeric spider between the mounting plate and the driven hub.
A less expensive and more axially compact armature assembly makes use of a so-called ring spring between the armature and the mounting area of the driven hub. The ring spring actually is a series of three generally circular and angularly spaced leaf spring sections which, due to their shape and location, provide some limited torsional dampening. In this type of an armature assembly, separate non-magnetic bumpers or spacers also must be provided between the armature and the mounting area of the driven hub in order to isolate the armature magnetically from the hub.